As a person detection technique for detecting the position(s) of a person(s) who is present inside an area, a technique of detecting the position of a person from an image captured by using a camera has been proposed in Japanese Unexamined Patent Application Publication No. 11-311682. In this method, the position of a person is detected by comparing an image captured by using a camera with a background image that has been prepared in advance. In a known method of this kind, a heat image captured by using an infrared camera is used, and the image is compared with a background temperature, thereby detecting the position of a person.
On another front, a technique of detecting the position of a person(s) who is the target of detection on the basis of a signal transmitted from a portable wireless terminal that has an RFID or GPS function, etc. and is carried by the target person, without using any image, has been proposed in Japanese Unexamined Patent Application Publication No. 2008-112257. In a known method of this kind, the position of a person is detected on the basis of the intensity of a signal (radio wave) transmitted from a wireless terminal. In another known method of this kind, a wireless terminal notifies its own GPS-detected position by means of a signal.